The present invention relates to a photographic information generating apparatus for a camera.
In a recent camera exposure control circuit, a complementary MOS (to be referred to as CMOS hereinafter) digital IC circuit is used which consumes only small amount of power to allow use of batteries and which can operate at a low voltage, and a shutter speed which is manually set at high precision is controlled in accordance with an output from an oscillator including a quartz oscillator.
In such a system, various photographic information is supplied to the CMOS digital IC circuit in the form of digital signals corresponding to the ON/OFF states of a group of switches connected to the input terminals of the CMOS digital IC circuit by a preset dial interlocked with the switches. The photographic information includes information indicating whether the selected mode is the automatic exposure control photographic mode or the manual exposure control photographic mode, and the information indicating the manually set shutter speed when the manual exposure control photographic mode is selected.
In this case, the input terminals of the CMOS digital IC circuit are gates of MOS transistors. Therefore, in order to keep constant potentials at the input terminals connected to the switches which are turned off, these input terminals must be pulled up or pulled down with resistors or the like. However, when the switches connected to the input terminals are ON, the pull-up or pull-down resistors are connected to the positive power source line and the ground line of an electrical shutter control circuit. Therefore, the current consumption of the electrical shutter control circuit is partially attributed to the resistors.
In order to minimize the current consumption of the electrical shutter control circuit, the impedances of the pull-up or pull-down resistors must be increased. However, when the impedances are increased, noise reduction characteristics are degraded. In particular, in a camera, noise which is generated in a synchronizing contact circuit for synchronizing an electronic flash device to the camera is very high. When the input terminals of the CMOS digital input circuit to which switches turned on or off in synchronism with a photographic mode setting dial are connected, are subjected to this noise, the photographic mode is erroneously set to a mode which is different to one set by the dial.